It is well known to use unmanned aerial vehicles (UAVs) in order to deliver payload to a predetermined area, and then either place the payload within that area or to disperse it therein. UAVs are useful in applications where the payload must be delivered to an area which is inaccessible or hazardous to human beings. Such UAVs are used for a variety of applications, such as dispersion of fire extinguishing material over a fire site, delivery of supplies (medical, food and otherwise) to inaccessible areas, cloud seeding applications, etc.